This invention relates to an apparatus for cooling oil or other fluid or coolant which is used to carry heat away from an X-ray tube in a computed tomography (CT) diagnostic imaging system. More particularly, the invention is directed to an apparatus and method which will facilitate reducing the amount of patient time required to perform an examination using the CT diagnostic imaging system.
As is well known in the art, an X-ray tube generates substantial amounts of heat in the course of its operation. Accordingly, provision must be made for removing heat from the proximity of the tube and for dispensing the heat into the surrounding environment. In a common arrangement, a coolant fluid or oil, circulates around the tube to receive excessive heat and then flows through a conduit to a heat exchanger. In the past, the heat exchanger caused the heat stored in the oil to be exposed to the surrounding air, so that the heat can be convected thereinto. The coolant oil then flows back to the tube through a second conduit.
Cooling arrangements of the above type commonly employ a fan to move air past or through the heat exchanger, to enhance heat transfer. If the X-ray tube is used in connection with a CT system, the tube, the heat exchanger, and the cooling fan are respectively mounted on an annular gantry, which is rapidly rotated around the patient to acquire a CT image. The gantry may rotate, for example, at a minimum of 90 revolutions per minute. At present, the X-ray tube cooling fans used in CT systems tend to be axial. That is, both the intake and exhaust air streams generated by the fans are directed along the fan axis (i.e., the axis of blade rotation). To provide sufficient cooling power, axial cooling fans must be rotated at a speed on the order of 3600 revolutions per minute. The axial fans typically force the air through at least one planar radiator that was situated in the path of airflow.
Attempts have been made in the past to reduce the amount of noise and vibration caused by the axial cooling fan systems of the past. For example, U.S. Pat. No. 5,956,383 issued to Kendall discloses a radial fan arrangement for cooling an X-ray tube mounted on the gantry of a CT system. In that reference, the axis of the fan is maintained in parallel relationship with the axis of the gantry to prevent gyroscopic loading of the fan as the fan rotates about the gantry axis with the gantry.
Another problem with CT is that the cost is high. To reduce the cost per patient, there is a desire to reduce the time required to take an X-ray by increasing the operational speed of the CT system. Increasing the speed also means that the patient does not have to remain still as long to get the same image, which results in improved results. Faster processing of patients further results in higher patient throughput.
In the past, the rotational speed of the gantry of CT system increased from one revolution/second to three revolutions/second, which required more X-rays to maintain the same rate of X-rays per unit time to get the same image. This, in turn, resulted in an increase in the power requirements of the CT system, thereby requiring an increase in the cooling requirements of the cooling system in the CT system.
As the rotational speed increased, the gravitational and gyroscopic forces increase, which means that the weight of the components must be reduced while the power is increased. Therefore, the need for lighter weight radiators, fans and pumps in the CT system became important. The space available for heat exchangers in the gantry of a typical CT system is limited.
One of the problems with the prior art devices, such as the Kendall device, was that the planar radiators did not perform a cooling as quickly as desired and could not easily accommodate increases in cooling requirements.